The field of the present invention is optical scanning of high-resolution color images, and in particular, the use of a flat-bed scanner system for the scanning of reflective and transmissive original documents at high resolution in a high volume production environment typical in the graphic arts electronic prepress industry. The original documents scanned by such systems include color or monochrome photographs, artwork, and composed pages of text and graphics. The actual graphic image content of the scanned original document is referred to as an "original".
In use of a flat-bed scanner for reflective scanning, an original on an opaque substrate is placed with the surface containing the original facing down on a flat transparent reference surface, typically glass. The original document is fixed on the surface such that a single line of the original, herein after referred to as a "scan line" is illuminated from below, and the light reflected from the scan line is directed through an optical system to form an image of the scan line on a sensor such as a CCD array, which converts the optical signal to an electronic representation of the scan line, comprising a line of digital picture elements, or "pixels". The desired portion of the original is scanned, one scan line at a time, by moving the original relative to the illumination system, optical system, and sensor along a direction hereinafter referred to as the "scanning axis". In systems typical of the prior art, such as that disclosed in U.S. Pat. No. 5,341,225, the illumination system, optical system and sensor are configured to move together as a unit. In other systems, such as those of U.S. Pat. No. 5,140,443, the original is moved while the illumination system, optical system and sensor remain fixed. In a production environment, original documents are scanned in a sequence, with each requiring a preparation step in which the original to be scanned is located and fixed on the surface in proper alignment and registration, followed by the actual scanning operation.
A transparent original document, typically a photographic transparency, comprises an original on one side of a thin transparent substrate. In this case, the original is illuminated from the side opposite from that containing the optical system and sensor. Use of a single flat-bed scanner for both types of scanning involves a modal configuration change. Typically, a flipcover used in reflective scanning mode to hold the original document flat on the transparent surface is replaced by a transmissive illumination module which illuminates from above the portion of the original to be scanned. As in reflective-mode scanning, prior art systems are configured so that either the original or one or more scanner illumination, optics or sensor components move to carry out the scanning process.
In addition to reconfiguration of the illumination system, the magnification of the optical system is typically changed so that the same number of pixels imaged on the CCD array, and captured by the digitizing electronics, corresponds to a larger or smaller area of the original. In high-resolution scanning systems typically in use in graphic arts electronic prepress processing, transparencies are oftentimes scanned at resolutions of 4,000 pixels per inch (ppi) or greater, while reflective originals are usually scanned at much lower resolutions, for example 1,200 ppi. Accordingly, in a production environment in which both reflective and transmissive originals are to be scanned in a mixed processing sequence, mode changes involving illumination system and resolution settings can add significantly to the time required for job processing.
It is therefore a general object of the present invention to provide an apparatus for high-volume, high-resolution color scanning for both reflective and transmissive original documents.
It is a specific object of the invention to provide a scanning apparatus wherein reflective and transmissive original documents can be intermixed in processing order with minimum system reconfiguration.
It is a further specific object of the invention to minimize the time during which the scanning apparatus must await original document preparation and setup for the next scan.
It is a feature of the invention that transmissive original documents can be prepared for a next scanning operation without interrupting a scanning operation currently in process.
It is another feature of the invention that positioning a transmissive original document in the scanning apparatus automatically selects operational parameters for transmissive scanning, and its removal restores the operational parameters for reflective scanning.
It is still another feature of the invention to provide visual aids for the accurate positioning and alignment of a reflective original to be scanned to minimize the time required for original document setup in reflective mode.